Batch preparation method of ultra-flat copper-nickel alloy single crystal wafer

Abstract

The invention discloses a batch preparation method of ultra-flat copper-nickel alloy single crystal wafers, and belongs to the field of preparation of single crystal alloy materials. According to the method disclosed by the invention, the batch preparation (more than 10 pieces) of 4-inch-level copper-nickel single crystal wafers is realized on the sapphire substrate on the basis of double-layer magnetron sputtering based on nickel first and copper second in cooperation with a batch preparation process of a slot type multi-piece annealing carrier, and the method has the remarkable advantages that the alloy proportion can be regulated and controlled, the crystal orientation is consistent, the surface roughness is lower than 1 nm and the like. According to the method disclosed by the invention, not only can the interface orientation and diffusion behavior be accurately regulated and controlled, but also the urgent requirements of multiple fields such as electronic interconnection, catalytic electrochemistry and two-dimensional material epitaxy on the high-performance Cu-Ni single crystal wafer can be met.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of single crystal alloy material preparation, in particular to a batch preparation method of ultra-smooth copper-nickel alloy single crystal wafer. BACKGROUND

[0002] Copper-nickel alloy has important value in many high-end fields due to its good metal film forming property, thermal stability and controllable alloy ratio. In particular, Cu-Ni(111) single crystal surface has extremely high lattice matching degree with various two-dimensional materials (such as graphene, h-BN, transition metal sulfide), making it an ideal substrate for the epitaxial growth of two-dimensional materials. As an epitaxial growth substrate for two-dimensional materials, Cu-Ni(111) surface has similar lattice constants to graphene, h-BN and other two-dimensional materials, and can achieve high-quality epitaxy through slight strain. At the same time, due to the interface advantage of single crystal, single-crystallized Cu-Ni substrate has no grain boundary scattering, and the surface has no steps and polycrystalline particles, providing more uniform catalytic activity and defect-free spreading channel during the growth of two-dimensional films. Currently, there are studies that have obtained 10 cm 2 The single crystal graphene film and ultra-smooth h-BN thin layer above have better device process consistency than polycrystalline substrates.

[0003] In addition, copper-nickel single crystal can also be used for catalysis and electrocatalysis reactions. Cu-Ni alloy electrodes can achieve high selectivity reduction of CO2 by virtue of the synergistic effect of bimetallic, and maintain long-term electrolytic stability.

[0004] However, the current preparation of large-size, high-orientation, and surface ultra-smooth copper-nickel single crystal substrate still faces the following technical bottlenecks: (1) It is difficult to achieve high-orientation single crystal domain structure by co-sputtering copper-nickel alloy, and after annealing, polycrystalline or small crystal domains are often formed, affecting the lattice quality of two-dimensional materials; (2) Traditional single-piece annealing method has low efficiency, small output, and uneven annealing environment, which is difficult to realize industrialization; (3) The difference in diffusion rate of copper and nickel elements during high-temperature annealing process leads to the formation of holes or delamination on the surface of the material, affecting the flatness and crystal continuity of the substrate.

[0005] Therefore, it is urgent to develop a new process route that can realize controllable and batch preparation of large-size, high-orientation, and ultra-smooth copper-nickel alloy single crystal wafer. SUMMARY

[0006] The application aims to provide a batch preparation method of ultra-smooth copper-nickel alloy single crystal wafers.

[0007] The application provides a batch preparation method of copper-nickel alloy single crystal wafers, comprising the following steps: (1) performing high-temperature annealing treatment on a c-oriented single-side polished sapphire wafer in a pure oxygen atmosphere; (2) depositing a nickel film on the surface of the annealed c-oriented single-side polished sapphire wafer by magnetron sputtering; (3) depositing a copper film on the nickel film in step (2) by magnetron sputtering to obtain a wafer on which a copper-nickel film is deposited; (4) loading multiple wafers on which a copper-nickel film is deposited into a slot-type wafer carrier, and then performing high-temperature annealing to obtain the copper-nickel alloy single crystal wafer; The slot-type wafer carrier is a frame-type container made of quartz material; parallel slots are arranged on the inner wall of the frame of the slot-type wafer carrier and used for supporting quartz plates; The wafer on which a copper-nickel film is deposited is placed on a quartz plate, and a piece of graphite is placed between the wafer on which a copper-nickel film is deposited and the quartz plate, and the graphite is used for supporting the wafer on which a copper-nickel film is deposited.

[0008] In the above method, the gap between the quartz plates is 10-30 mm; The length, width and thickness of the graphite are 5-8 mm, 5-8 mm and 2-5 mm, respectively; The graphite is placed at the center of the wafer on which a copper-nickel film is deposited; The slot-type wafer carrier is a cuboid frame-type container; The parallel slots are arranged at equal intervals on the inner wall of the frame of the slot-type wafer carrier; The quartz plate is provided with a groove for fixing the graphite.

[0009] In the above method, in step (2), the conditions for depositing the nickel film by magnetron sputtering are as follows: The background vacuum is less than or equal to 2x10 -5 Pa, 20-30 sccm of argon gas is introduced, the power of the power supply is 100-150 W, and the sputtering thickness of the nickel film is 50-150 nm; In step (3), the conditions for depositing the copper film by magnetron sputtering are as follows: The background vacuum is less than or equal to 2x10 -5Pa, 20-30 sccm argon is introduced, the power of the power supply is 100-200 W, and the sputtering thickness of the copper film is 250-450 nm.

[0010] In the method, the temperature of the high-temperature annealing in step (1) is 1100-1200℃, and the time is 1-3 h.

[0011] In the method, the high-temperature annealing in step (4) is performed in a 6-inch tube furnace. Specifically, the high-temperature annealing is performed under the following conditions: The 6-inch tube furnace is a three-zone tube furnace, which is first heated to 650-700℃ at a rate of 20-30℃ / min, and then heated to 1000-1100℃ at a rate of 10-15℃ / min for annealing, and the heating rates of the left and right zones are the same as that of the middle zone; the temperature of the middle zone is always 20-30℃ higher than that of the left and right zones during the whole heating process. The annealing time is 2-4 h. The annealing is performed in a mixed atmosphere of argon and hydrogen. The annealing is performed at normal pressure.

[0012] In the method, the volume ratio of argon to hydrogen is 1-3:1, and the flow rate of the mixed atmosphere is 2000-5000 sccm.

[0013] In the method, after the high-temperature annealing in step (3), there is a step of cooling to 650-700℃ at a rate of 5-20℃ / min, and then naturally cooling to room temperature.

[0014] In the method, in step (4), the number of pieces is 10 or more.

[0015] The Cu / Ni alloy ratio is obtained by adjusting the thickness of the nickel layer in step (2) and the thickness of the copper layer in step (3), and the atomic ratio of nickel to copper can be adjusted in the range of 10:90 to 30:70.

[0016] The application further provides a copper-nickel alloy single crystal wafer prepared by the above method.

[0017] The copper-nickel alloy single crystal wafer can be used as an epitaxial growth substrate for two-dimensional materials such as graphene or hexagonal boron nitride.

[0018] The copper-nickel alloy single crystal wafer is suitable for CVD epitaxial growth of single-crystal graphene or epitaxial growth of single-crystal hexagonal boron nitride (h-BN), and has wide application prospects in the fields of integrated circuit devices, heterojunction devices, wafer-level packaging, etc.

[0019] The application has the following advantages: (1) This invention provides a double-layer magnetron sputtering method of nickel first and copper later, combined with the slot-type multi-carrier annealing method, which can realize the batch preparation of 4-inch copper-nickel single crystal wafers (more than 10 wafers) on sapphire substrates. It has significant advantages such as adjustable alloy ratio, consistent crystal orientation and surface roughness of less than 1 nm. (2) Due to the strong interfacial interaction between nickel and c-axis single-sided polished sapphire wafers, the first deposited nickel layer is beneficial to inducing a single crystal orientation. (3) Copper has a higher diffusion rate in nickel. The copper position in the structure can effectively avoid the formation of interface pores and improve the continuity and density of the film. (4) The slot-type wafer carrier used in this invention can realize multi-wafer simultaneous annealing, and has good process repeatability and industrial expansion potential.

[0020] (5) The copper-nickel alloy single crystal wafer prepared by the present invention can meet the requirements of different two-dimensional materials for catalytic properties and thermal stability. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the slot-type wafer carrier structure of the present invention.

[0022] Figure 2 This is a physical image of the slot-type wafer carrier of the present invention.

[0023] Figure 3 This is a schematic diagram of wafer placement and annealing conditions within the tube cavity of a tubular furnace.

[0024] Figure 4 The images show a physical photograph of a copper-nickel alloy single-crystal wafer and a crystal orientation distribution diagram obtained from EBSD testing.

[0025] Figure 5 Physical images and characterization data of copper-nickel alloy single-crystal wafers prepared in batches for Example 1; Figure 5 (A) is a physical image; (B) is an X-ray diffraction pattern of 10 copper-nickel single crystals; (C) is a φ scan pattern; and (D) is a white light interference characterization pattern.

[0026] Figure 6 Characterization of the single crystallinity of copper-nickel alloy single-crystal wafers; among which, Figure 6 In the diagram, (A) represents the 2θ scan in HRXRD; (B) represents the φ scan in HRXRD.

[0027] Figure 7 Statistics on the single crystallinity of copper-nickel alloy single crystal wafers; among which, Figure 7 In the image, (A) represents the single crystallization statistics; (B) represents the optical micrograph of the single crystal region; and (C) represents the optical micrograph of the twinned region.

[0028] Figure 8Atomic force microscopy characterization and roughness statistics of the copper-nickel alloy single-crystal wafer prepared in this embodiment; wherein, Figure 8 (A) is an atomic force microscopy characterization image; (B) is a roughness statistic.

[0029] Figure 9 This is a schematic diagram of the sputtering mechanism for different sputtering sequences.

[0030] Figure 10 Results of copper-nickel alloys prepared by different sputtering methods (Example 1, Comparative Example 1, and Comparative Document 2); wherein, Figure 10 In the example, (A) is the copper-nickel alloy single crystal wafer prepared in Example 1; (B) is the wafer prepared in Comparative Example 2; and (C) is the wafer prepared in Comparative Example 1. Detailed Implementation

[0031] The present invention will be further described in detail below with reference to specific embodiments. The embodiments given are only for illustrating the present invention and are not intended to limit the scope of the present invention.

[0032] Unless otherwise specified, the experimental methods described in the following examples are conventional methods.

[0033] Unless otherwise specified, the quantitative experiments in the following examples are all repeated three times, and the results are averaged.

[0034] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0035] The schematic diagram of the slot-type wafer carrier used in the following embodiments is shown below. Figure 1 See actual product photos Figure 2 The slot-type wafer carrier of this invention is a cuboid frame structure made of high-purity quartz material. This material selection ensures excellent stability, a low coefficient of thermal expansion, and extremely high cleanliness at temperatures exceeding 1000°C, preventing the introduction of metal contamination during annealing and thus guaranteeing the crystallization quality of the copper-nickel alloy thin film.

[0036] The slotted wafer carrier has multiple parallel slots inside for inserting quartz plates. Specific capacities are as follows: Lateral capacity: The width (W) of the carrier is designed to be slightly greater than 4 inches (approximately 120 mm), which can perfectly accommodate and hold a four-inch wafer.

[0037] Longitudinal capacity: The carrier's length (L is 400cm) is designed to accommodate three four-inch wafers side by side.

[0038] Vertical capacity: The height of the vehicle (H is 50cm) is designed to allow for the simultaneous insertion of up to 5 independent quartz plates.

[0039] Therefore, the maximum processing capacity of this carrier is 5 layers × 3 pieces = 15 four-inch wafers, achieving extremely high space utilization and batch processing efficiency.

[0040] Each support structure is a flat quartz plate with three pre-set grooves for positioning graphite blocks. The graphite blocks (5 mm × 5 mm × 3 mm) are used to support the wafers, ensuring that the wafers remain stable in the horizontal direction and preventing them from sliding, colliding or sticking during loading, unloading and annealing.

[0041] On the inner walls of both sides of the slot-type wafer carrier frame, precision parallel slots matching the thickness of the aforementioned quartz plates are machined. These slots are arranged at equal intervals, ensuring that each layer of quartz plates remains absolutely horizontal and parallel to each other after insertion, thereby guaranteeing a consistent spatial gap between layers (adjustable from 10 mm to 30 mm, specifically 30 mm in this embodiment). This gap is carefully calculated to maximize space utilization while ensuring uniform flow of hot air between wafers, resulting in uniform heating of all wafers. This is crucial for obtaining highly consistent single-crystal materials within a batch.

[0042] Example 1 (1) Preparation of c-plane sapphire Ten 4-inch, single-sided polished sapphire wafers (the 4-inch single-sided polished sapphire wafers were purchased from Jiangyin Lanke Crystal Materials Co., Ltd., with a thickness of 650±25 μm) were taken and sequentially acid-washed (concentrated sulfuric acid and concentrated phosphoric acid were mixed at a volume ratio of 3:1), thoroughly rinsed with ultrapure deionized water to remove all acid residues, and dried with nitrogen.

[0043] The cleaned sapphire wafer was annealed at 1100°C for 3 hours in a pure oxygen atmosphere, and then cooled before being taken out for use.

[0044] (2) Preparation of Ni / Cu bilayer thin films by magnetron sputtering The annealed sapphire wafer was placed in a magnetron sputtering vacuum chamber and evacuated to a vacuum level of 2 × 10⁻⁶. -5 Pa; then sputter a nickel target (99.99% purity), with an argon flow rate of 20 sccm, a power setting of 150 W, a sputtering time of 500 s, and a nickel layer thickness of approximately 50 nm; Switch to copper target (99.99% purity) sputtering, power set to 100 W, sputtering time 3600 s, deposited copper layer thickness approximately 450 nm; After completing the double-layer sputtering, the gas supply was stopped, the wafer was allowed to cool naturally to room temperature, and the carrier was removed to obtain a wafer with a copper-nickel thin film deposited on it.

[0045] (3) High-temperature annealing alloying and recrystallization Ten wafers with deposited copper-nickel thin films were loaded into the same slotted wafer carrier (the wafers with deposited copper-nickel thin films were placed on a quartz plate, with a graphite block placed between them, the graphite block at the center of the wafer). The carrier, along with the wafers, was placed in the central region of a 6-inch tube furnace (model: BTF-1200C-III-3ZL-CVD, Anhui Beiyike Equipment Technology Co., Ltd., three temperature zones). Under a mixed atmosphere of argon and hydrogen (argon to hydrogen volume ratio 3:1), the argon and hydrogen flow rates were 3000 scmm and 1000 sccm, respectively. The temperature of the middle temperature zone was set 30°C higher than that of the left and right temperature zones to create a temperature gradient difference during annealing, providing a driving force for the growth of single-crystal domains. First, the intermediate temperature zone is rapidly heated at a rate of 30°C / min. Then, the left and right temperature zones are opened and heated at the same rate as the intermediate zone, maintaining the temperature of the intermediate zone 30°C higher than that of the left and right zones throughout the heating process. The intermediate temperature zone is heated to the recrystallization temperature of the copper-nickel metal film, 700°C, and then further heated to the annealing temperature of 1100°C at a rate of 10°C / min. The annealing time is 3 hours, and the pressure is atmospheric pressure.

[0046] After the heat preservation is completed, the three temperature zones are cooled at a rate of 10°C / min. When the middle temperature zone is cooled to 700°C, the three temperature zones are then naturally cooled to room temperature to prepare a copper-nickel alloy single crystal wafer.

[0047] A schematic diagram of wafer placement and annealing conditions within the tube furnace cavity is shown below. Figure 3 .

[0048] Figure 4 Here are physical images of the copper-nickel alloy single-crystal wafer prepared in this embodiment and crystal orientation distribution diagrams obtained by EBSD testing; from Figure 4 It can be seen that sampling analysis was performed at six locations on the prepared copper-nickel alloy single-crystal wafer. The out-of-plane (IPF) characterization results of EBSD all showed a uniform blue color, and the color distribution was concentrated on the (111) crystal plane, proving that the wafer prepared in this embodiment has good single crystallization in the out-of-plane direction. At the same time, the EBSD characterization results of the non-twinned copper-nickel alloy single-crystal wafer in the in-plane x-axis (RD) and in-plane y-axis (TD) directions also showed consistent colors, and its in-plane crystal plane orientation distribution was very concentrated, with no difference between the six locations. The above results prove that the copper-nickel alloy single-crystal wafer prepared in this embodiment has a strictly single-crystal structure both in-plane and out-of-plane.

[0049] The prepared copper-nickel alloy single-crystal wafers were characterized by optical microscopy, XRD, and white light interferometry. The crystal orientation uniformity was over 95%, the surface RMS was <1 nm, and the yield was over 95%. Figure 5 ).

[0050] The following are some points to note regarding the process: During sputtering, the substrate temperature must be kept below 50°C to avoid excessive initial stress on the thin film. During the annealing heating process, it is recommended to use three-zone temperature control and control the movement of the furnace body to separate the heating and cooling zones and ensure temperature uniformity. Gas flow rate and purity have an important impact on oxidation inhibition and grain growth. When removing the carrier, the pressure must be released slowly to avoid sudden stress changes that could cause the wafer to crack.

[0051] Figure 6 The single-crystallinity of the copper-nickel alloy single-crystal wafer prepared for this embodiment was characterized. In the 2θ scan of HRXRD, only the (0006) peak of sapphire and the (111) peak of CuNi were present, indicating that the copper-nickel alloy single-crystal wafer has a (111) crystal plane. By performing a φ scan on the sample, selecting the (200) peak of the CuNi thin film and the (0224) peak of the sapphire, it was found that CuNi and sapphire each had a set of three peaks spaced 120° apart, proving that the nickel alloy single-crystal wafer does not contain twins and is a single crystal.

[0052] Figure 7 The single crystallinity of the copper-nickel alloy single-crystal wafer prepared in this embodiment was statistically analyzed. Using an optical microscope, 60 regions of the entire 4-inch wafer were examined, with 5 samples taken from each region. It was found that only 2 regions were twinned, while the rest were single-crystal regions without twinned structures. The single crystallinity of each region was statistically analyzed by area, and the single crystallinity of the prepared copper-nickel alloy single-crystal wafer was above 99%.

[0053] Figure 8 Atomic force microscopy characterization and roughness statistics of the copper-nickel alloy single-crystal wafer prepared for this embodiment were performed. The surface roughness of the copper-nickel alloy single-crystal wafer was characterized at 10 × 10 μm. 2 The surface of the copper-nickel alloy single-crystal wafer is very smooth, with no grain boundaries. The average roughness of 40 sites on the copper-nickel wafer was also statistically analyzed, and it was only 0.45 nm, meeting the requirement of RMS < 1 nm.

[0054] Comparative Example 1 The preparation method and conditions are the same as in Example 1, except that copper is sputtered first, followed by nickel.

[0055] Comparative Example 2 The preparation method and conditions are the same as in Example 1, except that copper and nickel targets are sputtered simultaneously during the magnetron sputtering process, with the base vacuum set to 2 × 10⁻⁶. -5 Pa, 20 sccm of argon gas was introduced, the power of the copper target was 200 W, the power of the DC power supply corresponded to a sputtering rate of 6 nm / min, the power of the nickel target was 50 W, corresponding to 1.5 nm / min; the total sputtering thickness was 500 nm.

[0056] Figure 9 This is a schematic diagram of the sputtering mechanism. It can be seen that sputtering nickel first results in uniformly oriented OR I domains on the sapphire. Then, sputtering copper onto the nickel film, followed by high-temperature annealing, yields a single-crystal copper-nickel alloy. However, sputtering copper first or co-sputtering copper-nickel produces two types of antiparallel OR I and OR II domains, which form twin boundaries between the two grown domains after high-temperature annealing. Therefore, to obtain a single-crystal copper-nickel alloy wafer, a nickel-first, copper-later double-layer magnetron sputtering method is required.

[0057] Figure 10 Results for copper-nickel alloys prepared by different sputtering methods. Figure 10 It is evident that the sputtering sequence and method are crucial for the activity of copper-nickel single crystals. Since copper and nickel fuse at different rates at high temperatures, with nickel diffusing into copper at a faster rate, sputtering nickel first facilitates the diffusion of lower-layer nickel into the copper bulk phase, effectively preventing the formation of volatilization pores. Simultaneously, sputtering nickel onto the sapphire surface promotes the formation of a single OR-I orientation, preventing the formation of twin boundaries after high-temperature annealing and resulting in large-area single crystals.

Claims

1. A method for batch preparation of copper-nickel alloy single-crystal wafers, comprising the following steps: (1) The c-axis single-sided polished sapphire wafer is subjected to high-temperature annealing in a pure oxygen atmosphere; (2) A nickel film was deposited on the surface of a single-sided polished sapphire wafer in the c-direction after annealing by magnetron sputtering; (3) A copper thin film is deposited on the nickel thin film described in step (2) by magnetron sputtering to obtain a wafer with a copper-nickel thin film deposited on it; (4) Load multiple wafers with deposited copper-nickel thin films into a slot-type wafer carrier, and then perform high-temperature annealing to obtain the copper-nickel alloy single crystal wafer; The slotted wafer carrier is a frame-type container made of quartz material; the inner wall of the frame of the slotted wafer carrier is provided with parallel slots for inserting quartz plates. The wafer with the deposited copper-nickel thin film is placed on a quartz plate, and a graphite is placed between the wafer and the quartz plate to support the wafer with the deposited copper-nickel thin film.

2. The method according to claim 1, characterized in that: The gap between the quartz plates is 10-30 mm; The graphite has a length, width, and thickness of 5-8 mm, 5-8 mm, and 2-5 mm, respectively. The graphite is placed at the center of the wafer on which a copper-nickel thin film has been deposited; The slotted wafer carrier is a rectangular frame container. The slotted wafer carrier has parallel slots arranged at equal intervals on the inner wall of its frame.

3. The method according to claim 1 or 2, characterized in that: In step (2), the conditions for magnetron sputtering deposition of nickel thin films are as follows: Background vacuum less than or equal to 2 × 10⁻⁶ -5 Pa, 20-30 sccm of argon gas is introduced, the power supply is 100-150 W, and the nickel film sputtering thickness is 50-150 nm; In step (3), the conditions for magnetron sputtering deposition of copper thin films are as follows: Background vacuum less than or equal to 2 × 10⁻⁶ -5 Pa, 20-30 sccm of argon gas is introduced, the power supply is 100-200 W, and the sputtering thickness of the copper thin film is 250-450 nm.

4. The method according to any one of claims 1-3, characterized in that: In step (1), the high-temperature annealing temperature is 1100-1200℃ and the time is 1-3 h.

5. The method according to any one of claims 1-4, characterized in that: In step (4), the high-temperature annealing is carried out in a 6-inch tube furnace; Specifically, the conditions for high-temperature annealing are as follows: The 6-inch tube furnace is a three-zone tube furnace; firstly, the middle zone is heated to 650-700℃ at 20-30℃ / min, and then annealed at 1000-1100℃ at 10-15℃ / min. The heating rate of the left and right zones is the same as that of the middle zone. Throughout the heating process, the temperature of the middle zone is always kept 20-30℃ higher than that of the left and right zones. The annealing time is 2-4 hours; The annealing is carried out in a mixed atmosphere of argon and hydrogen; The annealing pressure is atmospheric pressure.

6. The method according to claim 5, characterized in that: The volume ratio of argon to hydrogen is 1-3:1; The flow rate of the mixed atmosphere is 2000-5000 sccm.

7. The method according to any one of claims 1-6, characterized in that: Step (3) involves cooling the temperature to 650-700°C at a rate of 5-20°C / min after high-temperature annealing, and then allowing it to cool naturally to room temperature.

8. The method according to any one of claims 1-7, characterized in that: In step (4), the number of pieces is 10 or more.

9. A copper-nickel alloy single-crystal wafer prepared by the method according to any one of claims 1-8.

10. The application of the copper-nickel alloy single crystal wafer of claim 9 as a substrate for epitaxial growth of two-dimensional materials.

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